When viscous materials such as adhesive, sealant, or paint are filled into a cylindrical container such as a drum, it is common practice to fill the viscous materials into an inner bag after loading the inner bag into the drum so as to prevent the viscous materials from adhering to the inner surface of the drum; otherwise the drum would not be reusable.
FIG. 5 shows the structure of the conventional inner bag used for this purpose. This inner bag, indicated by reference numeral 50, generally comprises a cylindrical portion 54 and a circular sheet 56 forming the bottom of the inner bag 50. The cylindrical portion 54 consists of two rectangular sheets 52 which are bonded together at two side edges, indicated by 53, by heat-seal techniques. The circular sheet 56 is further bonded to the cylindrical portion 54 at the periphery 58 of the bottom also by heat-seal techniques.
The manner in which the viscous materials are filled into and discharged from the inner bag 50 as described above is illustrated in FIGS. 6(a)-6(e). FIGS. 6(a)-6(e) show that a sequence of steps-begins-with installing of the inner bag 50 in the cylindrical drum and ends with discharging the viscous materials from the inner bag. This sequence of steps is hereinafter described briefly. A pump for filling under pressure the viscous materials toward the bottom of the drum, indicated by 23, has a follower plate 31. The inner bag 50 is installed at its one end on the follower plate 31. Under this condition, the viscous materials, indicated by 27, are filled into the inner bag 50, as shown in FIG. 6(a). Then, the other end 11 of the inner bag 50 is closed to form a closed portion 12, as shown in FIG. 6(b). The drum 23 is inverted so as to overlap a separate drum 24, and the inner bag 50 of the drum 23 is transferred into the separate drum 24 in such a manner that the closed portion 12 of the other end 11 of the inner bag 50 is brought into contact with the bottom of the separate drum 24, as shown in FIG. 6(c). Subsequently, the drum 24 is closed with a top cover 26, as shown in FIG. 6(d). When the viscous materials 27 are discharged at a consumer's site, the top cover 26 is removed and then the bottom 21 of the inner bag 50 is cut with a cutter knife or the like to form an opening. The viscous materials 27 are discharged through a central opening 33 of the follower plate 31 of the pump, as shown in FIG. 6(e).
A reason why the viscous materials 27 are filled into and discharged from the inner bag by the method described above is follows. In the case where the viscous materials 27 are a moisture-curing resin, air remaining in the closed portion of the other end 11 of the inner bag 50 and moisture in the air serve to cure surface portions of the viscous materials 27 which are located in adjacent to the closed portion. Therefore, the inner bag 50 of the drum 23 is transferred to the separate drum 24 in the inversion manner, that is, is turned upside down. Accordingly, the uncured portion of the materials which are in the bottom of the inner bag 50 of the drum 23 can be discharged firstly.
In addition, in the case where the conventional cylindrical inner bag 50 as described above is utilized, following problems are occurred. As shown in FIG. 5, the inner bag 50 is fabricated by bonding the cylindrical portion 54 to the circular sheet 56 forming the bottom at the periphery 58 of the bottom by heat-seal techniques. The cylindrical portion 54 is obtained by bonding together the two rectangular sheets 52 at two side edges by heat-seal techniques. Therefore, it is difficult to subject the circular sheet 56 to a heat-seal operation. Sometimes, some portions of the sheet do not sufficiently undergo the heat-seal operation. In this case, when the inner bag is kept in stock or being delivered to consumer's site, air containing moisture enters the inner bag 50, as a result of which there is a possibility that the moisture-curing resin on the bottom 21 as well as the resin in the closed portion 12 is cured. Furthermore, the heat-seal operation is difficult to carry out. This results in an increase in the cost.
When the cylindrical inner bag 50 accommodating the viscous materials 27 and loaded on the cylindrical container such as a drum is transferred into other drum, if one tries to invert the loaded drum in order to transfer the inner bag 50, any gap is not easily formed between the outer periphery of the inner bag and the inner wall of the drum, due to the fact that the inner bag 50 has a cylindrical contour which is substantially coincided with that of the drum. Therefore, the bottom portion of the loaded drum is placed in a vacuum condition. Hence, the inner bag 50 is not easily dropped off from the inverted drum. In this way, it is difficult to transfer the inner bag.
With this conventional art inner bag 50, the permeability of air deteriorates the quality of the viscous materials 27. The cost is increased because it is difficult to perform the heat-seal operation. Furthermore, the transfer operation is not carried out efficiently. These are problems in the conventional technique.